1. Field of the Invention
The present invention relates to thread connected pipe joints such as those used in the oil and gas well industry including for example oil well tubing, casing, line pipe and drill pipe (all of which will be referred to hereinafter as "pipe" or "pipe joints"). Even more particularly, the present invention relates to an improved method and apparatus for detecting wear at pin and box joints that can include dovetail, wedge and/or taper type thread connections.
2. General Background of the Invention
In the oil and gas well drilling industry and in the production of oil and gas, it is common to employ a number of joints of pipe that are connected end-to-end for purposes of communicating with oil and gas that is contained deep in the earth. These lengths of pipe can be used for drilling and/or production purposes.
For many years, oil well drill pipe and like pipe joints used a standard pin and box connection that included transverse faces or annular shoulders that would engage upon assembly of a pair of joints. These abutting faces created a seal.
Recently, pin and box type connections and similar type connections have been developed that form a seal with the interlocking threads of the pin and box connections. In such a situation, because the pin and box threads form a seal, there is no need for abutting annular shoulders, transverse faces or annular faces to form a seal. Indeed, the transverse end portions or stand-off surfaces of the joints do not touch unless the threads are badly worn.
One of the problems facing a user of such pipe joints is that the wear can be very gradual. It is important that the operator know when the wear has reached a level requiring replacement.
A number of patents have issued for pin and box type connections that use threaded connections such as dovetail, wedge threads, taper threads and the like. Some of these patents disclose stand off surfaces, i.e., any two transverse surfaces that are spaced apart upon assembly. An example of such a patent is the Blose patent 4,161,332, entitled "Dovetail Connection for Pin and Box Joints". In the Blose '332 patent, a pipe joint includes pin and box members having interengaged two step threads and interengaged annular shoulders preventing radial and axial separation of the members.
The Blose patent 4,192,533 discloses a pipe joint pin and box connection wherein the pin and box member have interengagable two step threads and interengagable annular shoulders for preventing radial and axial separation of the members.
The Ortloff patent 4,703,954 discloses a threaded pipe connection of the wedge shaped thread type that avoids high stress concentrations in the box between the first thread and the end of the box by making the length of the box between the first thread and the end of the box equal to or greater than 5% of the pipe diameter and by providing clearance between the crest of the first full thread on the box and the root of the last thread on the pin and between the crest of the last full thread on the pin and the root of the first full thread on the box.
A metal-to-metal wedge thread coupling connector is the subject of the Reeves patent 4,712,815.
The Mott patent 5,454,605 discloses a tubular connection having interlocking wedge threads. A threaded pipe connection that discloses a coupling used to join two pin members is the subject of U.S. Pat. No. 5,794,985. A reissue of the Reeves '409 patent is reissue patent 34,467, entitled "Tubular Connection".